This month marks a year since the deaths of 16 prized polo ponies in the back of a truck that travelled across Bass Strait on Tasmania's premier tourist ferry, and there are still more questions than answers.

As the Spirit of Tasmania saddles up again as a major sponsor of this year's Barnbougle Polo in the state's north-east, a persistent cloud hangs over the deaths and subsequent investigation that has sparked widespread condemnation from animal rights experts, a Victorian court case and talk of a potential criminal prosecution.

The ponies, from the Willo Polo club in New South Wales, perished somewhere between northern Tasmania and a rural Victorian property after disembarking from the Spirit Of Tasmania in Melbourne on January 29 last year, while on the journey home from Barnbougle.

The Spirit of Tasmania's sponsorship of the annual event is at the heart of its defence to Mr Williams's lawsuit — if the case goes to trial, it will in the first instance argue the sponsorship rendered void any liability over the pony deaths.

Mr Williams has claimed the ponies died during the voyage from Devonport to Melbourne and TT-Line failed to provide a safe environment, checks or airflow.

Meanwhile, TT-Line is accusing him of failing to ensure the truck was suitable, failing to have regard for the weather, failing to ensure the ponies were housed in individual stalls, and failing to ensure they had proper ventilation.

The state-owned company is also claiming it was Mr Williams who failed to check or inspect the horses before driving onto the ferry, and driving off again in Melbourne.

But Mr Williams says TT-Line accepted his truck and the ponies as safe for passage on its ferry, and would not have done so unless it was safe.

Which brings us to the question of checks and just who is responsible for ensuring animals that travel across Bass Strait are alive and well at the time of the journey.

Calls for investigation findings to be released to the public

As horse owners, veterinarians, media outlets and many in the broader community continue to call for answers from authorities in the public interest, the civil court case, which won't be heard before a jury, and possible others, which may be, have been cited by those authorities as the reason for their continued silence on the autopsy results or other details of the investigation.

Barnbougle Polo organiser Richard Sattler this week added his voice to the calls, saying he was "disappointed" it had taken so long to reveal how the ponies died.

"It's 12 months now," he said.

"People have been left with unknown answers to questions that everyone's asked."

Tasmania's Department of Primary Industries (DPIPWE) is the lead investigator, meaning it's a government department primarily responsible for probing a government business that is also a major sponsor of a blue-chip Tasmanian event with natural links to the state's primary industries circles.

Under a grilling by Opposition MPs at last month's Government Business Enterprise (GBE) hearings, in which former senior government minister Rene Hidding accused Greens leader Cassy O'Connor of "trying to prejudice a court case against the people of Tasmania", former primary industries minister Jeremy Rockliff denied the department's silence had left a cloud hanging over TT-Line.

TT-Line chairman Mike Grainger told the hearing he was annoyed his company had to "suffer this brand damage" associated with ongoing alarm about animal safety on the ferries and said he had seen no evidence, nor conclusive information that the ponies died en route.

He said repeatedly he was "confident the company is not at fault" and promised it would "vigorously defend this court action".

But Mr Grainger also said he'd not been provided with information from DPIPWE and he and company CEO Bernard Dwyer acknowledged TT-Line crew, while conducting watch on decks, "don't check the animals themselves" because "most horse or livestock owners would not want us to do that" and rely on a consignment note for animal counts.

When pressed on whether the note was visually cross-checked against the number of animals onboard a vehicle and whether they were alive, the company said it would need to take the question on notice and that it needed to be careful what it said because of the court action.

But if the company has not been provided with information by the investigating department, as the chairman said, and did not check the ponies before, during or after the voyage, is it possible to rule out that they perished while on its vessel?

As for DPIPWE Biosecurity Tasmania staff, it's not clear whether they checked the ponies or any other livestock travelling across Bass Strait.

The ABC has been told there have been regular occurrences on weekends in recent months in which there were no Biosecurity Tasmania staff inspecting freight vehicles disembarking from the Spirit of Tasmania at Devonport.

And according to leaked minutes from the June meeting of the Bass Strait Livestock Shipping Committee, "biosecurity officers no longer go out to inspect animals for fit to load". The minutes also noted biosecurity inspectors could only offer advice and were "unable, under law" to make the decision.

Viewing platform infrastructure, suggested more than 18 months ago "to allow inspection of livestock contained within trailers" at Devonport was yet to occur, the minutes noted, in part due to "insufficient space" and possible "transport delays".

In a statement, DPIPWE said it was not aware of having missed any inspections.

"Biosecurity Tasmania has rigorous systems in place to ensure it is aware of livestock and produce entering the state via the Spirit of Tasmania and other sea-based freight carriers," the statement read.

"Manifests are supplied to Biosecurity Tasmania the day before any vessel's arrival, and documentation for livestock is also supplied the day before arrival to ensure compliance with entry requirements. If there is any issue with documentation, animals are ordered into isolation for follow-up by a senior livestock officer.

"On weekdays and Saturdays Biosecurity Tasmania staff man the interstate container inspection regime to coincide with the arrival of the Spirit in Devonport. On Sundays, there is not a high volume of freight arriving by sea and it generally remains on the wharf until Monday.

"On Sundays, Biosecurity Tasmania staff conduct a visual check of the freight yard and also have access to the freight manifests in order to check what is arriving."

Transport regulations not mandatory

National standards for land transport of livestock, such as three-hourly inspections, do not apply to livestock being transported on a sea-going vessel.

And as for the Victorian side of the equation, its Department of Agriculture has formulated an Animal Welfare Guidance Document for the Transport of Livestock across Bass Strait.

Created after the pony deaths, it states that shipping companies are responsible for animal welfare on accepting them for loading, and "in the event of animal ill health or mortality during the passage or upon arrival", the shipping company will be responsible for "the proper treatment, removal or disposal of livestock".

It also states shipping staff are to have adequate training, including being competent to practice "euthanasia and managing animal welfare emergencies" and that the ship master is to be ultimately responsible and "ensure that all deaths and downers during any voyage on Bass Strait are reported to the relevant state animal health authority".

The document rules air flow should not be obstructed by other vehicles and not be positioned near motors or refrigeration units, that arrangements must be made at destination ports for the humane unloading of injured animals, and "all livestock must be inspected at port and assessed for fitness to proceed on the road journey".

"Downer [collapsed] animals must not be subjected to onward transportation unless authorised by a veterinarian in writing … any adverse events or observations must be recorded," it states.

When contacted by the ABC, a spokeswoman for the Victorian department said the guidance document was designed as advice only, meaning it is not mandatory and not legally enforceable.

The Bass Strait Livestock Shipping Committee comprises of a number of DPIPWE representatives, as well as industry figures and the RSPCA.

Tasmanian shipping identity Les Dick, livestock buying company HW Greenham and Sons and employee Graeme Pretty are also on the committee, despite being prosecuted by DPIPWE on aggravated animal cruelty and other charges over the deaths of more than 60 cattle that travelled across Bass Strait three years ago.

Mr Pretty was confirmed as chairman of the committee at the June meeting.

All parties have consistently denied the charges and the court case has previously been delayed.

All of which raises more questions.

One of the only certainties is those 16 ponies died a horrible death that no-one would have wished to happen. But it did.